{On this wise} (hout(9373)). A free quotation from  Ge 15:13 .
{Should sojourn} (estai paroikon). Shall be a sojourner,
Paroikos (para, beside, oikos, home), one dwelling near
one's home, but not of it, so a stranger, foreigner, old word,
often in LXX, temporary residence without full rights of
citizenship ( 7:29  13:17 ), and descriptive of Christians ( Eph
2:19  1Pe 1:17  2:11 ). {In a strange land} (en g(8869) allotri(8369)).
In a land not one's own, that belongs to another, alien as in  Mt
17:25f. , which see. {Four hundred years} (et(8820)tetrakosia).
Accusative of duration of time. As in  Ge 15:13 , but a round
number as in  Ex 12:40  the time is 430 years. But in  Ga 3:17 
Paul, following the LXX in  Ex 12:40 , takes the 430 years to
cover the period in Canaan and the stay in Egypt, cutting the
sojourn in Egypt to about half. Josephus gives it both ways.
Hackett suggests two solutions, one that there were two ways of
reckoning the period among the Jews with no way of settling it,
the other that by the 430 years in Egypt the writers meant to
include Canaan also as merely the preliminary to the period in
Egypt.